Disposable, moisture vapour permeable, liquid impermeable covering sheet for bedding articles having an improved comfort

ABSTRACT

Disposable covering sheet for bedding articles that is moisture vapour permeable and liquid impermeable and comprises at least a moisture vapour permeable fibrous layer and a liquid impermeable but moisture vapour permeable film layer of preferred thermoplastic compositions. Use of the disposable covering sheet as, for example, a mattress or pillow cover provides increased comfort to the user. The disposable covering sheet disclosed herein can be used in a variety of applications, particularly when the benefits of moisture vapour permeability, liquid imperviousness, disposability and increased in-use comfort are desired.

CROSS REFERENCE TO PRIOR APPLICATION

[0001] This is a continuation of International ApplicationPCT/US01/24860, with an international filing date of Aug. 7, 2001,published in English.

FIELD OF THE INVENTION

[0002] The present invention relates to a disposable covering sheet forbedding items such as mattresses, pillows, etc. which is moisture vapourpermeable and liquid impermeable and comprises improved liquidimpermeable formed structures having an enhanced moisture vapourpermeability comprising thermoplastic compositions preferably appliedonto a moisture vapour permeable substrate. The covering sheet of thepresent invention can find a variety of applications wherein moisturevapour permeability, liquid imperviousness, disposability, and comfortare desirable. Preferably the covering sheet of the instant invention isa mattress cover or a pillow cover.

BACKGROUND OF THE INVENTION

[0003] Covering sheets for bedding articles, particularly bed mattresscovers, are known in the art. A primary use of these articles is toprotect mattresses, particularly bed mattresses, but also pillows,cushions, duvets, upholstery, from contaminants, e.g. from dust,liquids, or bodily fluids, for example in environments where a mattressis intended to be used by different users, such as in hospitals, hotels,or rental houses. Furthermore, mattress covers are used in house forproviding a mattress with a protective covering.

[0004] More recently mattress covers have been also proposed to act asan allergen barrier to control house mites that live in the dust,typically on and within mattresses where they can find favourableenvironmental conditions in terms of temperature and nourishment.

[0005] It has long been established that house mites, also known as dustmites, are a source of house dust allergens that not only causeallergies, but also adversely contribute to other pathologies, such asasthma. It has also been established that use of allergen controlmeasures is effective in controlling these conditions. Allergen-proofencasing to contain mites to prevent allergen egress has long been usedin mattresses, such as bed mattresses, pillows, cushions, duvets,upholstery.

[0006] Mattress covers come in direct or indirect (i.e. through furtherintermediate layers, e.g. bed sheets, or pillowcases) contact with thehuman body, therefore it is important that such covers are moisturevapour permeable for comfort reasons, in addition to being liquidimpermeable in order to provide the mattress with the desired protectionagainst external agents. When used as a barrier against dust mites theyshould also have an allergen barrier capability.

[0007] Various examples of disposable mattress covers which are at thesame time liquid impermeable and breathable, i.e. moisture vapourpermeable, are known in the art.

[0008] Known disposable mattress covers comprise different materials orstructures which are capable of providing a liquid barrier, in additionto providing moisture vapour permeability, preferably air permeability.Such structures or materials can comprise a single layer, or multiplelayers laminated together. An example are structures comprisingthermoplastic microporous films, e.g. laminated to fibrous layers suchas nonwoven layers.

[0009] Particularly preferred materials which are suitable fordisposable mattress covers are hydrophilic continuous films, also knownas “monolithic films”, that do not allow the flow of moisture vapourthrough open pores or apertures in the material, but do transfersubstantial amounts of moisture vapour through the film by absorbingwater on one side of the film where the moisture vapour concentration ishigher, and desorbing or evaporating it on the opposite side of the filmwhere the moisture vapour concentration is lower.

[0010] In our patent applications EP 0963760 and EP 0964026thermoplastic compositions are disclosed for making hydrophiliccontinuous moisture vapour permeable, liquid impermeable layers havingpreferred characteristics of moisture vapour permeability and liquidimperviousness. The disclosed preferred thermoplastic compositions arealso readily processable so as. to provide a coating having the desiredthickness onto a substrate, so avoiding the need of complex traditionalextrusion apparatuses. This is achieved by modifying the viscosity ofthe thermoplastic polymers by means of the inclusion in the compositionof a suitable plasticiser or blend of plasticisers that lowers suchviscosity. This allows to utilise with these preferred compositionstypical process conditions known in the art for the direct coating oflow viscosity hot melt compositions onto a substrate in order to form amoisture vapour permeable, liquid impervious film or layer.

[0011] Disposable, moisture vapour permeable, liquid impermeablemattress covers comprising a moisture vapour permeable, liquidimpermeable structure, which in turn comprises a layer of thethermoplastic compositions according to either EP 0963760 or EP 0964026,preferably applied onto a moisture vapour permeable substrate, e.g. afibrous layer such as a nonwoven layer in order to form a compositestructure, are particularly preferred since they provide better moisturevapour permeability combined with liquid imperviousness, and also takeadvantage of the increased ease of manufacture associated to the abovementioned compositions.

[0012] Another improvement to disposable mattress covers is described inour European patent application No. 99124535.8, filed on Dec. 9, 1999,where an increased friction is established between the disposablemattress cover and the mattress surface during the use, when i.e. themattress cover is typically subjected to a certain compression againstthe mattress itself, in order to minimise possible misplacements of thecover during its use, for example when the mattress is a bed mattress ora pillow, and the mattress cover can be moved or misplaced by the user'smovement, e.g. during the sleep. This is particularly important when themattress cover is intended for partial covering of the external surfaceof a mattress, for example of the upper surface of a bed mattress, e.g.,in combination with traditional means for connecting the cover to themattress, such as for example elastic bands or strands applied at thecorners of a rectangular bed mattress cover.

[0013] Provision of an increased friction between the mattress cover andthe mattress is however also useful in the context of a mattress coverintended for total encasing of a mattress. In both cases in fact thisincreased friction prevents or at least reduces relative movementsbetween the mattress cover and the mattress during the use, thereforehelping in keeping the mattress cover in its right position providedinitially, e.g. by the user when applying the cover to the mattress.

[0014] Even if the bedding items disclosed in our above mentioned patentapplications function well, particularly in terms of protection, it wassurprisingly discovered by selecting some parameters of the componentsconstituting the bedding articles of the present invention as thereafterindicated, and preferably by using certain thermoplastic compositionsfor the hydrophilic continuous layer comprised in the bedding article,as described in the European patent application having the title“Thermoplastic hydrophilic polymeric compositions with improved adhesiveproperties for moisture vapour permeable structures” (P&G Case CM2406F,filed on the same day of the present invention) the comfort for the useris significantly increased compared to the prior art items, whileoffering the same or better protection.

SUMMARY OF THE INVENTION

[0015] A disposable, moisture vapour permeable, liquid impermeable,covering sheet for bedding articles comprising at least a moisturevapour permeable fibrous layer and a liquid impermeable but moisturevapour permeable film layer applied onto the fibrous layer, the coveringsheet having the following characteristics:

[0016] a Water Vapour Transmission Rate (WVTR) value of at least 400g/m²·24 h;

[0017] a Hydrostatic water Head (HH) value of at least 1 cm;

[0018] a ratio R of the caliper, expressed in micrometers, to the basisweight, expressed in g/m², of at least 2.5.

[0019] The Water Vapour Transmission Rate, the Hydrostatic water Head,and the caliper are measured according to the methods described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The drawings herein are intended to illustrate preferredembodiments of the present invention, but are not meant to limit in anyway its scope.

[0021]FIG. 1 is a schematic plan view of a disposable mattress coveraccording to the present invention.

[0022]FIG. 2 is a cross-sectional view of the disposable mattress coverof FIG. 1 taken along the line A-A.

[0023]FIG. 3 illustrates the mattress cover applied to a mattress.

DETAILED DESCRIPTION OF THE INVENTION

[0024] According to the present invention, a disposable, moisture vapourpermeable, liquid impermeable covering sheet for bedding articles isprovided which comprises at least a moisture vapour permeable fibrouslayer and a liquid impermeable but moisture vapour permeable film layercomprising a highly processable thermoplastic composition having anenhanced moisture vapour permeability. Said covering sheet offers anincreased comfort to the user, particularly when used as a mattresscover.

[0025] The term “mattress”, as used therein, refers to a fabric casefilled with resilient material, such as for example cotton, hair,feathers, foam rubber, or an arrangement of coil springs, and thereforecomprises particularly bed mattresses, but also pillows, cushions,comforters, duvets, upholstered portions of beds (such as headboards),or of sofas or armchairs. Consequently, even if the present inventionwill be described with particular reference to a disposable coveringsheet for bedding items in the form of a mattress cover, it is not meantto limit in any way its scope to mattress covers.

[0026] Referring particularly to mattresses it is generally known thateach mattress every year “absorbs” from about 45 kilos to about 80 kilosof sweat and about 150 grams of skin scales. In addition to this,millions of mites generally live in the mattress. Another problem isthat accidental staining is practically unavoidable. Usually consumersare aware of the above problems and, in fact, most of them use reusablemattress covers which usually are made from cotton. But these covers donot solve the above problems.

[0027] An ideal mattress cover should offer a number of benefits such asa superior protection, i.e. by constituting a barrier to stains, dust,allergens, and micro organisms; a superior in-use comfort, i.e. by beingbreathable or water vapour permeable (no sweat), by producing a lownoise in use, and by providing a softness sensation to the user; and asuperior ease of use, i.e. it by being disposable so as to avoid reuseand high temperature laundering.

[0028] It should be noted that disposability involves not only a lightand low cost structure but also an easy application, removal anddisposal.

[0029] Contrary to the prior art the present invention solves the aboveproblems by providing a disposable covering sheet for bedding articlesand particularly a disposable mattress cover with superior protection,superior in-use comfort, and ease of use.

[0030] The disposable covering sheet for bedding articles of the presentinvention consists in a laminate of different layers comprising at leasta first moisture vapour permeable layer and a second liquid impermeablebut moisture vapour permeable film layer of thermoplastic compositionbonded onto said first layer, i.e. the laminate consists of at least twobonded layers giving rise to a composite structure.

[0031] If more film layers of thermoplastic compositions are utilised ina composite structure in combination with one or more other moisturevapour permeable layers to create a layered moisture vapour permeable,liquid impermeable composite structure, each film layer can be made of asame specific thermoplastic composition according to the presentinvention, or of different specific thermoplastic compositions accordingto the present invention.

[0032] The above composite structure can involve at least one component,typically the film layer, of the thermoplastic composition incombination with one or more other moisture vapour permeable layers.Such moisture vapour permeable materials include, but are not limitedto: fibres, fibrous batts, non-wovens, wovens, papers, micro-porous orporous membranes, films such as polymeric films, perforated or aperturedfilms and papers, macroscopically expanded films, cloth, etc.

[0033] Said other components may be non-absorbent, absorbent,liquid-containing, etc.

[0034] The composite structures of the covering sheets described abovehave a moisture vapour transfer rate (WVTR) of at least 400 g/m²·24 h,more preferably at least 500 g/m²·24 h, and most preferably at least 600g/m²·24 h. They have a Hydrostatic water Head (HH) value of at least 1cm, preferably of at least 10 cm, and a ratio (R) of caliper, expressedin micrometers, to the basis weight (expressed in g/m²) of at least 2.5,preferably of at least 3.5.

[0035] According to a particularly preferred embodiment of the presentinvention the disposable, moisture vapour permeable, liquid impermeablemattress cover comprises a composite structure comprising a film layerof the thermoplastic composition applied onto a moisture vapourpermeable substrate, wherein said film layer is intended, in use, todirectly contact the mattress. The moisture vapour permeable substratepreferably comprises a fibrous layer, e.g. a nonwoven layer onto whichthe thermoplastic composition is applied in a continuous layer or filmby means of known means, e.g. preferably by hot melt coating.

[0036] A disposable, moisture vapour permeable, liquid impermeablemattress cover comprising a moisture vapour permeable, liquidimpermeable structure in turn comprising a layer of the thermoplasticcomposition according to the present invention which is intended, inuse, to directly contact a mattress, can have any shape and arrangementwhich is known in the art, and which is suitable for its intended use.

[0037] For example, if the mattress consists of a standard bed mattress,the mattress cover can be a substantially rectangular flat sheet withelastic strings at the corners, or alternatively with integrallyelasticised corners, as described in FR 2747899. The rectangular sheettypically has suitable dimensions in order to completely cover at leastthe upper surface of the bed mattress, and preferably, as in the latterembodiment referred to above, also the side surfaces thereof, whereinthe elastic strings or the elasticised corners provide for a suitablereleasable connection, in a way known in the art, to the mattress.Alternative configurations where the mattress cover has a suitable shapeand size in order to completely encase a mattress are also possible.This latter configuration could be preferred when the mattress cover, inaddition to liquid imperviousness and moisture vapour permeability,should also to provide a total barrier against dust mites and relatedallergens.

[0038] Preferably, as shown in the herein drawings, a disposablemattress cover comprises a rectangular blanket made according to thepresent invention. In particular, the disposable, moisture vapourpermeable, liquid impermeable blanket is formed by a topsheet 1, whichis a moisture vapour permeable fibrous layer, and a backsheet 2, whichis a liquid impermeable but moisture vapour permeable film layer of athermoplastic composition, according to the present invention, laminatedonto said topsheet 1 in order to form a two-layer composite structure.The backsheet 2 is intended to face and to be in direct contact with thetop of a mattress 4, while the topsheet 1 is intended to face the user.

[0039] The thermoplastic compositions of the present invention canprovide a certain degree of residual tackiness to the backsheet 2. Inturn, this tackiness prevents or at least reduces relative movementsbetween the mattress cover and the mattress 4 during use, thereforehelping in keeping the mattress cover in its right position provided bythe user initially. In any case and if preferred, the mattress cover canhave no residual tackiness by suitably selecting the thermoplasticcompositions according to the present invention or by neutralising anyresidual tackiness with known means, e.g. talcum powder.

[0040] For assisting the user to put the mattress cover on the mattressin the right position but also for fixing the mattress cover to themattress in a stable manner four adhesive means 3 are provided, as shownin the drawings. The adhesive means 3 can be one or more stripes of aconventional pressure sensitive adhesive covered by a release liner forprotecting the adhesive before use, as utilised, for example, in themanufacture of the panty fastening adhesive patch of commercial sanitarynapkins.

[0041] As shown in FIG. 3, the mattress cover has suitable dimensions tosubstantially or completely cover at least the top surface of themattress 4, while the adhesive means 3 are preferably attached to thelateral sides of the mattress 4.

[0042] Any other suitable shape or arrangement for a mattress coveraccording to the present invention is also possible, depending on theparticular mattress type, shape and dimensions, and on the intended useof the mattress cover.

[0043] Preferably the disposable, moisture vapour permeable, liquidimpermeable covering sheet for bedding articles of the presentinvention, when used as a mattress cover or a pillow cover, has asurface area ranging from 15.0 m² to 0.3 m², preferably from 8.0 m² to0.5 m². Most preferably, particularly in the case of a mattress cover,said surface area is from 4.0 m² to 1.0 m².

[0044] The Thermoplastic Compositions

[0045] According to a preferred embodiment of the present invention, thethermoplastic polymeric composition for making a moisture vapourpermeable, liquid impervious structure at least comprises athermoplastic hydrophilic polymer or a mixture of thermoplastichydrophilic polymers, and a suitable compatible hydrophilic tackifyingresin, or a blend of suitable compatible hydrophilic tackifying resins,in order to provide a thermoplastic polymeric hydrophilic compositionwith a desired degree of adhesiveness or tackiness in the molten,semi-molten, or plastic state, and/or in the stable state at roomtemperature.

[0046] In the following description the terms “adhesiveness” and“tackiness” are considered to be synonymous.

[0047] The terms “breathable” and “breathability” are intended herein tocorrespond to “moisture vapour permeable” or “water vapour permeable”,and “moisture vapour permeability” or “water vapour permeability”.“Moisture vapour” and “water vapour” are also considered to beequivalent.

[0048] Suitable thermoplastic hydrophilic polymers comprised in thecomposition according to the present invention include polyurethanes,poly-ether-amides block copolymers, polyethylene-acrylic acid andpolyethylene-methacrylic acid copolymers, polyethylene oxide and itscopolymers, ethylene acrylic esters and ethylene methacrylic esterscopolymers, poly lactide and copolymers, polyamides, polyesters andcopolyesters, polyester block copolymers, sulfonated polyesters,poly-ether-ester block copolymers, poly-ether-ester-amide blockcopolymers, polyacrylates, polyacrylic acids and derivatives, ionomers,polyethylene-vinyl acetate with a vinyl acetate content of more than 28%by weight, polyvinyl alcohol and its copolymers, polyvinyl ethers andtheir copolymers, poly-2-ethyl-oxazoline and derivatives, polyvinylpyrrolidone and its copolymers, thermoplastic cellulose derivatives,poly-caprolactone and copolymers, poly glycolide, polyglycolic acid andcopolymers, polylactic acid and copolymers, polyureas, and mixturesthereof.

[0049] Particularly preferred thermoplastic hydrophilic polymers arethermoplastic poly-ether-amide block copolymers (e.g. Pebax™),thermoplastic poly-ether-ester-amide block copolymers, thermoplasticpolyester block copolymers (e.g. Hytrel™), thermoplastic polyurethanes,typically non reactive polyurethanes (e.g. Estane™), or mixturesthereof.

[0050] The hydrophilic tackifying resin comprised in the thermoplastichydrophilic polymeric compositions according to this preferredembodiment of the present invention must have a high polar character,wherein said polar character is measured and expressed by means of asuitable polarity parameter.

[0051] When alternatively a blend of hydrophilic tackifying resins iscomprised in the thermoplastic hydrophilic polymeric compositions of thepresent invention, said blend must comprise at least 50% by weight of atackifying resin or resins having said high polar character. Preferablyeach hydrophilic tackifying resin of the blend has said high polarcharacter.

[0052] A suitable polarity parameter can be selected among parametersknown in literature which are useful to give a measure of the polarcharacter of a substance, for example in terms of its hydrophilicity orof its solubility, typically in water, measured by means of suitabletest methods. For example, known polarity parameters suitable formeasuring the polar character of a substance in the context of thepresent invention comprise the water absorption at equilibrium, or theHildebrand solubility parameter, or the contact angle with water, or thedual contact angle, which parameters are well known in physicalchemistry and are measurable according to known methods which can befound in the scientific and technical literature.

[0053] It has been discovered that a particularly suitable polarityparameter for measuring the polar character of a tackifying resinaccording to this preferred embodiment of the present invention is theequilibrium contact angle with water of the hydrophilic tackifyingresin, measured according to the Equilibrium Contact Angle MeasuringTest method described herein. The equilibrium contact angle with wateractually gives a measure of the hydrophilicity of a substance in termsof the interaction between that substance and a drop of water at acommon interface.

[0054] According to the present invention, the hydrophilic tackifyingresin has the required high polar character according to the presentinvention if it has an equilibrium contact angle with water not greaterthan 86 degrees, preferably not greater than 84 degrees, more preferablynot greater than 82 degrees, as measured according to the EquilibriumContact Angle Measuring Test described herein.

[0055] Alternatively, if a blend of compatible hydrophilic tackifyingresins is comprised in the thermoplastic hydrophilic polymericcomposition of the present invention, said blend must comprise at least50% by weight of a tackifying resin or resins having an equilibriumcontact angle with water not greater than 86 degrees, preferably notgreater than 84 degrees, more preferably not greater than 82 degrees, asmeasured according to the Equilibrium Contact Angle Measuring Testdescribed herein.

[0056] Preferably however, each compatible hydrophilic tackifying resinof such a blend should have the required high polar character expressedin terms of its preferred equilibrium contact angle with water asexplained above.

[0057] Suitable compatible hydrophilic tackifying resins, or blends ofhydrophilic tackifying resins, having the required high polar charactercompatible with the thermoplastic hydrophilic polymer or mixture ofthermoplastic hydrophilic polymers according to the present inventioncan be selected by the man skilled in the art among available tackifyingresins by measuring the value of the respective polarity parameter,namely the equilibrium contact angle with water as explained above, andaccording to the test method described herein. Suitable resins are forexample the tackifying resins produced by Hercules Inc. and availableunder the codes Res A-2690, Res A-2691, Res A-2682, Res A-2683, ResA-2698.

[0058] The selected preferred hydrophilic tackifying resin or blend ofhydrophilic tackifying resins having high polar character comprised inthe thermoplastic hydrophilic polymeric compositions of the presentinvention are generally such that, when such a hydrophilic tackifyingresin is added at a level of 30% by weight to a pure thermoplastichydrophilic polymer to form a two component thermoplastic hydrophilicpolymeric composition, the water vapour transmission rate (WVTR) of a 50μm thick continuous film formed from the thermoplastic hydrophilicpolymeric composition constituted by the hydrophilic tackifying resinand the hydrophilic polymer is at least 40%, preferably at least 50%,more preferably at least 60% of the WVTR value of a 50 μm thickcontinues film made of the pure hydrophilic polymer and not comprisingthe tackifying resin, wherein the WVTR values are measured according tothe modified ASTM E-96 “Upright Cup” Method. 30% by weight correspondsto a typical average addition level for a tackifying resin in thethermoplastic hydrophilic polymeric compositions of the presentinvention.

[0059] Preferably the thermoplastic hydrophilic polymeric compositionsaccording to the present invention comprise a blend of hydrophilictackifying resins, more preferably with each resin of the blend beingselected by means of the polarity parameter satisfying the conditions asdescribed above, wherein the blend comprises at least a hydrophilictackifying resin which is liquid at room temperature, since this isbeneficial to the processability of the thermoplastic hydrophilicpolymeric composition. Preferably not all the tackifying resins of sucha blend are however liquid at room temperature.

[0060] By saying “a tackifying resin liquid at room temperature” it isherein meant a tackifying resin having a softening point below 25° C.,wherein said softening point is evaluated according to the Ring and BallMethod ASTM E 28-67. Conversely a tackifying resin which is solid atroom temperature is a resin having a softening point above 25° C. Atemperature of 25° C. has been considered in this context toconventionally correspond to the “room temperature”.

[0061] The thermoplastic hydrophilic polymers or mixture ofthermoplastic hydrophilic polymers as mentioned above, comprised in thethermoplastic hydrophilic polymeric composition of the presentinvention, can be typically highly viscous in the molten state at theprocess conditions that are typical of the known processes of film orlayer formation, e.g. an extrusion process involving a high power screwextruder. For example they may have a viscosity higher than 5000 poiseat a temperature of 20° C. above the DSC (Differential ScanningCalorimetry) melting point, which is the temperature identified as thatcorresponding to the DSC peak, or corresponding to the highest DSC peakin case of a mixture of polymers showing more than one peak, and at afrequency of 1 rad/sec.

[0062] The thermoplastic hydrophilic polymeric compositions of thepresent invention, comprising the thermoplastic hydrophilic polymer(s)and the compatible hydrophilic tackifying resin(s), can therefore stillbe highly viscous in the molten state at the process conditions.

[0063] According to a preferred embodiment of the present invention, andas disclosed in our patent applications EP 0963760 or EP 0964026, theviscosity of the thermoplastic polymeric hydrophilic compositions of thepresent invention can be preferably adjusted by including in thethermoplastic hydrophilic polymeric composition a suitable plasticiser,or blend of plasticisers, that is also compatible with the thermoplastichydrophilic polymer or polymers and with the hydrophilic tackifyingresin or resins and that lowers the viscosity of the thermoplastichydrophilic polymeric composition in the molten state at the processconditions.

[0064] Viscosity of the thermoplastic hydrophilic polymeric compositionsof the present invention can therefore be adjusted by suitably selectingthe plasticiser, depending on how the composition is to be processed.For example film extrusion techniques can be suitably used withcompositions having higher viscosity at the process conditions, as it isknown in the art. Alternatively, suitable hot melt coating processes canbe preferred to process the compositions, as explained in the abovementioned patent applications EP 0963760 and EP 0964026. This impliesthat the viscosity in the thermoplastic hydrophilic polymericcomposition at the process conditions has to be adjusted at a suitablelower level.

[0065] In such a case, the thermoplastic polymeric hydrophiliccompositions of this alternative embodiment of the present inventioncomprise a suitable plasticiser or blend of plasticisers such that theypreferably have the following complex viscosities (η* ):

[0066] 50 poise<η*<4000 poise, preferably 100 poise<η*<2000 poise, morepreferably 100 poise<η*<1000 poise, at a frequency of 1 rad/s at atemperature of 210° C. or less and η*<2000 pose, preferably η*<1000poise, more preferably η*<500 poise, at a frequency of 1000rad/s at aprocess temperature (T) of 210° C. or less, wherein η* represents thecomplex viscosity of the thermoplastic polymeric hydrophiliccomposition. Preferably the temperature T is 200° C. or less and morepreferably 180° C. or less and most preferably from 200° C. to 50° C.

[0067] According to this preferred embodiment of the present inventionthe thermoplastic hydrophilic polymeric compositions having the complexviscosity described above allow for a film or layer to be coated onto asubstrate using typical coating conditions and apparatuses known in theart for the coating of low: viscosities hot melt compositions in a layerhaving a required thickness onto a; substrate, while, also keeping theadvantageous characteristics of the preferred thermoplastic hydrophilicpolymers in providing hydrophilic continuous moisture vapour permeable,liquid impermeable layers or films.

[0068] Thermoplastic hydrophilic polymeric compositions having suchviscosities can also provide very thin films or layers.

[0069] Suitable compatible plasticisers comprised in the thermoplastichydrophilic polymeric composition according to this preferred embodimentof the present invention include citric acid esters, tartaric acidesters, glycerol and its esters, sucrose esters, adipates, sebacates,sorbitol, epoxidized vegetal oils, polymerised vegetal oils, polyols,phthalates, liquid polyesters, glycolates, p-toluene sulfonamide andderivatives, glycols and polyglycols and their derivatives, sorbitanesters, phosphates, monocarboxylic fatty acids (C₈-C₂₂) and theirderivatives, and mixtures thereof.

[0070] According to a particularly preferred embodiment of the presentinvention particularly preferred plasticisers are hydrophilicplasticisers such as acids, esters, amides, alcohols, polyalcohols, ormixtures thereof, as disclosed in our application WO 99/64505. Saidparticularly preferred hydrophilic plasticisers have a particularly highpolar character and provide the further advantage that they do notimpair, and possibly can even enhance, the moisture vapour permeabilityof the resulting layer or film formed from the preferred thermoplastichydrophilic polymeric composition of the present invention comprisingsaid plasticiser or blend of plasticisers, when compared to acorresponding film or layer formed from a thermoplastic hydrophilicpolymeric composition comprising the same components, but without theplasticiser or plasticisers.

[0071] The particularly preferred hydrophilic plasticiser or blend ofhydrophilic plasticisers can of course also adjust the viscosity of thethermoplastic composition according to a preferred embodiment of thepresent invention to the preferred values in order to make itprocessable by coating said thermoplastic composition onto a substratein a film layer having a desired thickness.

[0072] Suitable preferred hydrophilic plasticisers according to thispreferred embodiment of the present invention comprise acids, esters,amides, alcohols, polyalcohols, or mixtures thereof, whereinparticularly preferred hydrophilic plasticisers are citric acid esters,tartaric acid esters, glycerol and its esters, sorbitol, glycolates, andmixtures thereof.

[0073] A suitable polarity parameter, such as one of those describedabove, can also be used in order to select the other components of thethermoplastic polymeric hydrophilic compositions of the presentinvention. Particularly, preferred thermoplastic hydrophilic polymersand, optionally, preferred compatible hydrophilic plasticisers can beselected for the thermoplastic polymeric hydrophilic compositions of thepresent invention by means of a suitable polarity parameter according tothe same principles already explained with reference to the compatiblehydrophilic tackifying resins. A same polarity parameter can be used toselect different components of the thermoplastic hydrophilic polymericcompositions of the present invention, or alternatively differentpolarity parameters for different components, as can be determined bythe man skilled in the art.

[0074] Preferably the thermoplastic polymeric hydrophilic composition ofthe present invention comprises from 10% to 99%, preferably from 20% to70%, more preferably from 30% to 50%, by weight of the thermoplasticpolymeric hydrophilic composition, of the thermoplastic hydrophilicpolymer or mixture of thermoplastic hydrophilic polymers, and from 1% to90%, preferably from 10% to 70%, more preferably from 20% to 50%, byweight of the thermoplastic hydrophilic composition, of the suitablecompatible hydrophilic tackifying resin or blend of hydrophilictackifying resins.

[0075] More preferably the thermoplastic polymeric hydrophiliccomposition of the present invention also comprises from 0% to 95%,preferably from 10% to 70%, more preferably from 20% to 50% by weight ofthe thermoplastic polymeric hydrophilic composition, of a suitablecompatible plasticiser or blend of suitable compatible plasticisers.

[0076] The thermoplastic hydrophilic polymeric compositions of thepresent invention may in addition comprise additional optionalcomponents to further improve the processibility of the compositions andalso the mechanical characteristics as well as other characteristics asresistance to ageing by light and oxygen, visual appearance etc., of thefilms or layers formed from such thermoplastic hydrophilic polymericcompositions.

[0077] A thermoplastic hydrophilic polymeric composition according tothe present invention can be manufactured with any known process thatwill typically comprise the steps of providing at least thethermoplastic hydrophilic polymer or mixture of polymers and thesuitable compatible hydrophilic tackifying resin or blend of compatiblehydrophilic tackifying resins, and optionally any further additionalcomponents as explained above, such as for example a plasticiser orblend of plasticisers, heating the components and compounding them, e.g.with a known suitable mixer to form the thermoplastic hydrophilicpolymeric composition in the molten state for subsequent process steps.

[0078] According to the present invention a moisture vapour permeable,liquid impervious layer can be formed from the thermoplastic hydrophilicpolymeric composition of the present invention, for example by layingsaid thermoplastic hydrophilic polymeric composition onto a substrate.The films or layers formed from the thermoplastic compositions of thepresent invention preferably have a moisture vapour transmission rate ofat least 400 g/m²·24 h, more preferably of at least 500 g/m²·24 h, evenmore preferably of at least 600 g/m² ·24 h, most preferably of at least1000 g/m²·24 h, with a thickness of said layer or film of at least 40μm, said water vapour transmission rate measured according to themodified ASTM E-96 “Upright Cup” Method. More preferably, the films orlayers as described above have the above preferred WVTR levels whereinthe thermoplastic hydrophilic polymeric composition comprises at least30% by weight of the hydrophilic tackifying resin, or of a blend ofhydrophilic tackifying resins, according to the present invention.

[0079] Other Characteristics

[0080] According to the present invention a moisture vapour permeable,liquid impervious layer can be formed from the thermoplastic compositionof the present invention by coating said thermoplastic composition ontoa substrate.

[0081] A process for making a film layer from a thermoplasticcomposition according to the present invention typically comprises thesteps of providing said composition, heating it to make it flowable, andcoating said composition in the molten state onto a substrate in a layerhaving the desired thickness. In accordance with the present invention,a moisture vapour permeable, water impervious composite is formed whichcomprises the thermoplastic composition and a substrate onto which saidthermoplastic composition is coated, wherein the substrate is alsomoisture vapour permeable.

[0082] Such embodiment provides a moisture vapour permeable, liquidimpervious composite structure wherein the film layer formed from thethermoplastic composition of the present invention is firmly bonded tothe substrate while providing the required performance for liquidbarrier and hence could be advantageously provided as thinly aspossible. In this manner such embodiment provides a moisture vapourpermeable, liquid impervious composite structure wherein thecontribution of the film layer formed from the thermoplastic compositionof the present invention to the performance of the composite materialresides mainly in the provision of a liquid barrier. The remainingperformance physical criterion being preferably provided by the providedsubstrate, that therefore preferably acts also as a support layer.However it should be noted that the film layer does not need to be asthin as possible in any application because the thermoplasticcompositions of the present invention provide high breathability (highWVTR) also in the case of thicker film layers. Typical thickness of thefilm layer of the thermoplastic composition applied onto a suitablesubstrate to form a composite structure according to the presentinvention range from 2 μm to 200 μm.

[0083] It should be appreciated that the above modalities of forming thecomposite structure in combination with the composition of the filmlayer according to the present invention, allow to provide a disposablecovering sheet for bedding articles offering a superior protection, asuperior in-use comfort, and an ease of use.

[0084] In particular, the preferred adhesiveness or tackiness impartedto the thermoplastic hydrophilic polymeric composition of the presentinvention by the addition of the compatible hydrophilic tackifying resinor blend of hydrophilic tackifying resins in fact typically provides foran increased adhesion of the film or layer in the molten, semi-molten,or plastic state to the substrate, for example a fibrous substrate suchas a nonwoven layer comprising hydrophobic synthetic fibres, while atthe same time keeping a high breathability of the film or layer, andhence preferably of the whole layered structure. This in turn provides abetter integrity of the resulting composite structure, which istherefore more resistant to e.g. delamination in use, also with verythin layers of the thermoplastic hydrophilic polymeric composition,wherein said improved adhesive properties of the composition and saidbetter resistance of the resulting composite structure are combined witha very limited, or no detrimental effect at all on the water vapourtransmission capability of the layer formed from the thermoplastichydrophilic polymeric composition of the present invention, for exampleif compared to a layer of the same thickness formed from a similarcomposition, not comprising the hydrophilic tackifying resin or blend ofhydrophilic tackifying resins of the present invention.

[0085] Furthermore preferred hydrophilic tackifying resins according tothe present invention can also increase the water vapour transmissionrate of a layer formed from the thermoplastic hydrophilic polymericcomposition of the present invention, when compared to a layer of thesame thickness formed from a similar composition, not comprising thehydrophilic tackifying resin or blend of hydrophilic tackifying resinsof the present invention.

[0086] The thermoplastic hydrophilic polymeric compositions for makingmoisture vapour permeable, liquid impermeable structures according tothe present invention have been so far described as being provided withthe desired adhesiveness or tackiness typically in the molten,semi-molten, or plastic state. This is desired in a preferred embodimentof the present invention in order to form e.g. more stable moisturevapour permeable, liquid impermeable layered composite structures withthe thermoplastic hydrophilic polymeric composition directly formed as alayer or film onto a suitable substrate, for example substrates having avery low polar character such as preferred nonwovens comprisinghydrophobic fibres, wherein said increased adhesiveness to a substrateis not achieved to the detriment of the moisture vapour permeability ofthe resulting layer or film.

[0087] However, the thermoplastic hydrophilic polymeric compositions ofthe present invention can also be formulated in order to have pressuresensitive adhesive character, i.e. such that the thermoplastichydrophilic polymeric composition remains tacky at any temperature.

[0088] The substrate, or support layer may be any useful layer which isalso moisture vapour permeable, preferably having a moisture vapourpermeability of at least 400 g/m²·24 h, more preferably at least 500g/m²·24 h, and most preferably at least 600 g/m²·24 h.

[0089] Preferred support layers for use herein include woven andnonwoven layers, most preferably hydrophobic fibrous layers such ashydrophobic nonwoven. As for non limiting examples, a SMS(Spunbonded-Meltblown-Spunbonded) hydrophobic 100% polypropylenenonwoven of 25 g/m² commercialised under the code MD3000 by Corovin—BBANonwovens Group (Germany), or a spunlaced nonwoven of 50 g/m²commercialised under the code TJET C500 by Tecnofibra (Italy) functionwell.

[0090] Suitable substrates for use herein as further layers in thestructure according to the present invention could also include twodimensional, planar micro and macro-porous films; macroscopicallyexpanded films; formed apertured films; nonwoven and woven layers.Suitable macroscopically expanded films for use herein include films asdescribed in for example in U.S. Pat. No. 4,637,819 and U.S. Pat. No.4,591,523.

[0091] The structures of the preferred embodiment according to thepresent invention are particularly advantageous as they allow thepossibility of providing a composite wherein the thermoplasticcomposition may be applied onto the support substrate as a film layerwith the desired thickness. Typical coating conditions and apparatusesknown in the art for the direct coating of low viscosities hot melts canbe readily utilised in order to provide the thermoplastic composition atthe desired thickness.

[0092] A possible method for forming a composite laminate by coating thethermoplastic composition onto a substrate acting as a support layer isdescribed in PCT application WO 96/25902.

[0093] At least at the coating temperature, the thermoplasticcomposition in form of a layer preferably exhibits adhesive propertieson the supportive substrate in order to form the preferred compositesuch that no additional adhesive is required to achieve a permanentattachment between the thermoplastic composition and the substrate.

[0094] A moisture vapour permeable, liquid impervious compositestructure formed by coating the thermoplastic hydrophilic compositionaccording to the preferred embodiment of the present invention onto asuitable substrate finds particular utility as a structure constitutinga disposable, moisture vapour permeable, liquid impermeable mattresscover according to the present invention.

EXAMPLE

[0095] A polyether-amide block copolymer available from Atofina (France)commercialised under the trade name Pebax 2533 SN is compounded with TriButyl Citrate (plasticiser) available from Aldrich Co., Res A-2691(tackifier resin) available from Hercules Inc., Res A-2690 (tackifierresin) available from Hercules Inc. and Irganox 1010 (anti oxidantagent) available from Ciba-Geigy.

[0096] The final formulation in percent by weight has the followingcomposition: 44% Pebax 2533 SN 25% Tri Butyl Citrate 15% Res A-2691 15%Res A-2690 1% Irganox 1010

[0097] The blend is melt extruded to obtain a film having a basis weightof 20 g/m². The film is laminated directly onto a substrate constitutedby a SMS (Spunbonded-Meltblown-Spunbonded structure) hydrophobic 100%polypropylene nonwoven 25 g/m² (support layer) commercialised under thetrade name MD3000, available form Corovin-BBA Nonwovens Group (Germany).The composite has a thickness 230 μm , a ratio R equal to 5.1, a WVTR of846 g/m²·24 h, and a HH value of 17 cm.

[0098] The composite structure is used to produce a mattress cover, e.g.a bed mattress cover as illustrated in the herein drawings. It has aflat rectangular shape with suitable dimensions to completely cover atleast the upper surface of a bed mattress, wherein the film layer 2 ofthermoplastic composition is intended to face, in use, the mattress 4,and to directly contact it. In particular, the dimension are: 1.64 m(width) and 1.96 m (length) to completely or substantially completelycover the upper surface of a bed mattress and partially its sides asindicated in FIG. 3. The four corners of the mattress cover are fixed tothe corners of the bed mattress by four adhesive stripes 3, afterdetaching the release liners 5 which protect the adhesive before use.The adhesive is a conventional pressure sensitive one as normally used,for example, in manufacturing the panty fastening adhesive of sanitarynapkins.

[0099] Comparison Results

[0100] The above disposable mattress cover was compared in internaltests to Intervent® which is a full encasing reusable mattress coverproduced by W. L. Gore & Associati S. r. L. (Italy) having a totalsurface area of 8.6 m² for a double bed mattress. Its thickness is 250μm, its basis weight is 130 g/m², and its ratio R is 1.92, its WVTR is2345 g/m²·24 h, and its HH is more than 300 cm.

[0101] Two internal tests, one for the evaluation of softness andanother for the evaluation of noise were conducted. Each test was adirect comparison between Intervent® and the mattress cover of thepresent invention. The test was conducted in the following manner:

[0102] 20 persons (P&G employees) were asked to make a sensorial andqualitative direct comparison of an A4 dimension (210×297 mm) sheet ofIntervent® (cut from it) and a same dimension sheet of the mattresscover of the present invention as illustrated in the example;

[0103] each person was asked to touch and handle the sheets (samples),first one per time and then together, while the sheets were hidden intwo boxes so that the person was unable to see them but only to touchthem for avoiding any influence due to any different visual appearanceof the two samples.

[0104] The sheets were changed with new ones after 3 people had testedthem;

[0105] at the end of each test the person gave his preference for thesample he preferred or expressed no preference for both of them.

[0106] There were performed two separate tests each involving 20 people,one was for noise and another for softness.

[0107] The following results were obtained: Absence of noise Softness(Preference) (Preference) Product according to 14 11 the presentinvention Intervent ® 4 6 No preference 2 3

[0108] It is evident from the above data the product according to thepresent invention was preferred for a better absence of noise and for abetter softness which, in turn, combined with the other characteristicsof the product according to the invention, give rise to a better in-usecomfort.

[0109] Tests Methods

[0110] According to the present invention the complex viscosity η* ismeasured using a Rheometer RDA-II available from Rheometrics Co.Moisture vapour permeability is measured as Water Vapour TransmissionRate (WVTR) at 25° C. and 55% relative humidity according to themodified ASTM E-96 “Upright Cup” method. The only modification to thestandard ASTM E-96 “Upright Cup” method consists in a change in theheight of the air gap between the sample and the water surface in thecup, which height is 3 mm±0.5 mm, instead of 19 mm±2.5 mm, as specifiedin the standard test method.

[0111] The softening point of the resins is measured according to theRing and Ball Method ASTM E28-67. Thickness or caliper is measuredaccording to the SCAN P-7:55 method. Hydrostatic water head value (HH)is measured according to the DIN 53886 method and reported in cm(centimetres).

[0112] Equilibrium Contact Angle Measuring Test.

[0113] The test method, which will be described hereinafter, is intendedto measure the equilibrium contact angle with water of a tackifyingresin intended to be comprised in a thermoplastic hydrophilic polymericcomposition according to the present invention. As it is known in theart, the contact angle is a measure of the phenomenon of wetting ornon-wetting of a solid by a liquid. The equilibrium contact angle ismeasured on a drop of liquid resting in equilibrium on the surface of asubstance, wherein the surface is horizontal. The angle between thebaseline of the drop and the tangent at the drop boundary is measured.

[0114] Apparatus

[0115] Climatically controlled laboratory maintained at 25° C. and 55%relative humidity.

[0116] Drop Shape Analysis System DSA 10 equipped with the VideoMeasuring System DSA 1 and DSA-Software Version 1.5 For Windows '95 NT.

[0117] Dosing unit G1023 with G1060 1 ml syringe and G1061 needle(having a length of 30 mm and a diameter of 0.5 mm).

[0118] Microscope glass slides 10 mm×30 mm.

[0119] Conditioning Oven

[0120] The system DSA 10 and the accessories DSA 1 with DSA-Software,G1023, G1060, G1061 are sold by Krüss GmbH, D 22453 Hamburg.

[0121] Preparation of the samples and contact angle measurements asdescribed below are conducted in the climatically controlled laboratory.

[0122] Sample Preparation

[0123] The preparation of the samples of the resins for the measurementof the equilibrium contact angle with water comprises the followingsteps:

[0124] 1. prepare a 10% by weight solution of the resin in a suitableorganic solvent. The high dilution provides a solution with a very lowviscosity. A suitable solvent must be selected which dissolves thetackifying resins to be used in the context of the present invention,and which also promptly evaporates. A suitable solvent must thereforehave a boiling point at atmospheric pressure not greater than 100° C.,preferably not greater than 80° C. Tetrahydrofuran has been selected asa particularly suitable solvent according to the present test method;

[0125] 2. completely dip a clean microscope glass slide (previouslythoroughly cleaned with methanol and dried) into the solution;

[0126] 3. remove the glass slide slowly from the solution and keep itvertical for about 10 seconds to obtain a uniform coating on bothsurfaces; the solvent almost immediately evaporates and leaves onto theglass surfaces a very thin, continuous layer of the resin having auniform thickness and a smooth surface; samples which do not possessthese features at a visual examination must be discarded;

[0127] 4. let the sample dry at air for about ten minutes withouttouching the surfaces;

[0128] 5. place the sample in the conditioning oven for at least 12 h ata temperature of 40° C. and 85% relative humidity;

[0129] 6. remove the sample from the conditioning oven and leave it coolin the climatic laboratory for about 20 minutes, until it reaches theroom temperature of 25° C.;

[0130] 7. measure the equilibrium contact angle; it is not relevant onwhich side of the glass slide the contact angle measurement is actuallyperformed, provided onto the selected side of the slide the resincoating is uniform and with a smooth surface, as explained under step(3).

[0131] Contact Angle Measurement

[0132] Contact angle measurements are performed with the Drop ShapeAnalysis System DSA 10 equipped with the Video Measuring System DSA 1with the DSA-Software, and the Dosing Unit G1023 with G1060 syringe andG1061 needle.

[0133] Liquid is distilled water used for HPLC (High Performance LiquidChromatography).

[0134] Measurements of equilibrium contact angle are conducted accordingto the standard usage instructions provided with the DSA 10 systemcomprising the respective accessories listed above.

[0135] The measurements are performed at air and at room conditions,i.e. at 25° C. and 55% relative humidity. The samples are positionedfollowing the usage instructions onto the sample stage of the DSA 10system.

[0136] The surface of the sample to be measured shall be horizontal.

[0137] A drop of water is positioned on the surface of the sample bymeans of the syringe G1060 with the G1061 needle. The drop volume has tobe duly controlled by means of the micrometer dosing screw of thesyringe such that the drop diameter ranges, between 1-2 mm. Within thisrange the contact angle is independent of the drop size.

[0138] The measurements of the equilibrium contact angle are conductedautomatically by the Drop Shape Analysis System DSA 10 with the VideoMeasuring System DSA 1 and the DSA-Software. The Video Measuring Systemrecords a movie sequence of the drop positioned onto the sample surface,and the measurement is actually performed on the first frame in whichthe drop stands still on the surface of the sample in order to have theequilibrium contact angle.

[0139] For each sample, from five to seven different measurements areperformed on different points of the surface. The highest and the lowestvalues obtained are discarded, and the remaining values are averaged, toensure a representative equilibrium contact angle value to be determinedfor each sample under investigation.

[0140] The very thin layer of resin formed onto the glass slideaccording to the described sample preparation procedure, provides for aneffective and reliable measurement of the equilibrium contact angle withwater not only for resins which are solid at room temperature, but alsofor resins which are liquid at room temperature, wherein “solid” and“liquid” at room temperature are to be intended according to thedefinition previously given in the description. In the latter case infact the glass slide provides the very thin resin layer of the samplewith an effective support, and avoids any detrimental effect which mightbe caused by the higher density of the water with respect to the resin.In other words, the combined effect of the very thin resin layersupported by the glass substrate, and of the very short time (fewseconds) needed for the automatic measuring of the equilibrium contactangle after the drop has been positioned onto the sample surface,prevents any possible deformation of the horizontal and flat resinsurface itself under the weight of the drop of water, and thereforeprovides for a correct equilibrium contact angle measurement.

What is claimed is:
 1. A disposable, moisture vapour permeable, liquidimpermeable, covering sheet for bedding articles, said sheet comprising:a. a moisture vapour permeable fibrous layer; and b. a liquidimpermeable but moisture vapour permeable film layer of thermoplasticcomposition applied onto said fibrous layer; wherein said covering sheetcomprises: a water vapour transmission rate value of at least about 400g/m²·24 h; a hydrostatic water head value of at least about 1 cm; and aratio R of the caliper, expressed in micrometers to the basis weight,expressed in g/m², of at least about 2.5.
 2. A disposable, moisturevapour permeable, liquid impermeable, covering sheet for beddingarticles according to claim 1 wherein said thermoplastic compositioncomprises: a. a thermoplastic hydrophilic polymer selected from thegroup consisting of polyurethanes, poly-ether-amides block copolymers,polyethylene-acrylic acid and polyethylene-methacrylic acid copolymers,polyethylene oxide and its copolymers, ethylene acrylic esters andethylene methacrylic esters copolymers, poly lactide and copolymers,polyamides, polyesters and copolyesters, polyester block copolymers,sulfonated polyesters, poly-ether-ester block copolymers,poly-ether-ester-amide block copolymers, polyacrylates, polyacrylicacids and derivatives, ionomers, polyethylene-vinyl acetate with a vinylacetate content of more than about 28% by weight, polyvinyl alcohol andits copolymers, polyvinyl ethers and their copolymers,poly-2-ethyl-oxazoline and derivatives, polyvinyl pyrrolidone and itscopolymers, thermoplastic cellulose derivatives, poly-caprolactone andcopolymers, poly glycolide, polyglycolic acid and copolymers, polylacticacid and copolymers, polyureas, and mixtures thereof; b. optionally, acompatible hydrophilic tackifying resin having an equilibrium contactangle with water no greater than about 86 degrees; and c. optionally, ablend of compatible hydrophilic tackifying resins, said blend ofcompatible hydrophilic tackifying resins comprising at least about 50%by weight of a tackifying resin or resins having an equilibrium contactangle with water no greater than about 86 degrees.
 3. A thermoplastichydrophilic polymeric composition according to claim 2, wherein saidequilibrium contact angle with water is no greater than about 84degrees.
 4. A thermoplastic hydrophilic polymeric composition accordingto claim 2, wherein said equilibrium contact angle with water is nogreater than about 82 degrees.
 5. A disposable, moisture vapourpermeable, liquid impermeable covering sheet for bedding articlesaccording to claim 2, wherein said thermoplastic composition furthercomprises a compatible plasticiser selected from the group consisting ofcitric acid esters, tartaric acid esters, glycerol and its esters,sucrose esters, adipates, sebacates, sorbitol, epoxidized vegetal oils,polymerised vegetal oils, polyols, phthalates, liquid polyesters,glycolates, p-toluene sulfonamide and derivatives, glycols andpolyglycols and their derivatives, sorbitan esters, phosphates,monocarboxylic fatty acids (C₈-C₂₂) and their derivatives, and mixturesthereof.
 6. A disposable, moisture vapour permeable, liquid impermeable,covering sheet for bedding articles according to claim 1, wherein saidwater vapour transmission rate is at least about 500 g/m²·24 h.
 7. Adisposable, moisture vapour permeable, liquid impermeable, coveringsheet for bedding articles according to claim 6, wherein said watervapour transmission rate is at least about 600 g/m²·24 h.
 8. Adisposable, moisture vapour permeable, liquid impermeable covering sheetfor bedding articles according to claim 1, wherein said hydrostaticwater head value is at least about 10 cm.
 9. A disposable, moisturevapour permeable, liquid impermeable covering sheet for bedding articlesaccording to claim 1, wherein said ratio R is at least about 3.5.
 10. Adisposable, moisture vapour permeable, liquid impermeable covering sheetfor bedding articles according to claim 1, wherein said hydrostaticwater head value is at least about 10 cm, and said ratio R is at leastabout 3.5.
 11. A disposable, moisture vapour permeable, liquidimpermeable, covering sheet for bedding articles according to claim 1,wherein said covering sheet is a disposable mattress cover or adisposable pillow cover having a rectangular shape and a surface areafrom about 15.0 m² to about 0.3 m².
 12. A disposable, moisture vapourpermeable, liquid impermeable, covering sheet for bedding articlesaccording to claim 11, wherein said covering sheet is a disposablemattress cover or a disposable pillow cover having a rectangular shapeand a surface area from about 8.0 m² to about 0.5 m².
 13. A disposablemattress cover according to claim 11 having a surface area from about4.0 m² to about 1.0 m².
 14. A disposable mattress cover according toclaim 13 having at least four adhesive means.